Earlier in the day, he bemoaned Mexican authorities' inability to stop the caravan.

Sadly, it looks like Mexico’s Police and Military are unable to stop the Caravan heading to the Southern Border of the United States. Criminals and unknown Middle Easterners are mixed in. I have alerted Border Patrol and Military that this is a National Emergy. Must change laws!

Muslim American advocates slammed Trump's statement as Islamophobic and racist.

The Council on American Islamic Relations (CAIR) accused Trump of pushing his agenda to create fear "regardless of truth, reality or morality".

"If he actually has evidence to support this racist and Islamophobic dog whistle, he should provide it to the public and explain why 'Middle Eastern' immigrants would be of particular danger to our nation," CAIR executive director Nihad Awad said in a statement.

"It is time for this president to be held accountable for his seemingly endless stream of lies and bigoted rhetoric."

Trump just claimed that there are "unknown Middle Easterners" mixed in with the Caravan that's heading to the Border.

1) If they are "unknown", how the hell do you know they are Middle Eastern?2) Middle Easterners are good people too!3) This is hateful, racist, rhetoric!

Abed Ayoub, the legal director of the American-Arab Anti-Discrimination Committee (ADC), said contrary to what the assertions of the administration are, migrants have a legal right to come to the border and claim asylum.

Not only are Trump's remarks unsubstantiated "fearmongering"; they are also racist, Ayoub said.

In a statement late on Sunday, Secretary of State Mike Pompeo said the migrants would not be allowed into the US. He raised concerns about the travellers being victimised by human smugglers, "violence provoked by some members of the group".

However, Pompeo made no mention of people from the Middle East in the travelling group.

"As President Trump has stated, consistent with US law, the United States will not allow illegal immigrants to enter or remain in the United States," the statement said.

Trump has made cracking down on immigration - both authorised and undocumented - a focal point of his campaign and presidency.

Trump kicked off his presidential candidacy in 2015 by describing undocumented Mexican immigrants as "rapists".

As a candidate, he also pledged to ban Muslims from entering the United States. And shortly after taking office he imposed a ban on several Muslim-majority countries that was upheld by the supreme court earlier this year.

In January, the US president was rebuked for decrying immigration from Haiti and African nations, which he referred to as "shithole countries".